[From string (line 14) ]                                                         
                                                                                 
@startuml                                                                        
[*] --> Active                                                                   
                                                                                 
state Active {                                                                   
  state fork1 <<fork>>                                                           
  state join1 <<join>>                                                           
                                                                                 
  [*] -> P1                                                                      
  P1 -> fork1                                                                    
  fork1 -> P2                                                                    
  P2 -> P1                                                                       
  --                                                                             
  [*] -> C1                                                                      
  C1 -> join1                                                                    
^^^^^                                                                            
 The state join1 has been created in a concurrent state : it cannot be used here.